JP2008530964A - Effective electromagnetic compatibility filter for machine tools - Google Patents

Abstract

【Task】
An EMC filter for a machine tool exhibiting low leakage current and having a production cost lower than that of a known device and more compact than that of the known device is provided.
[Solution]
Machine tool effective electromagnetic compatibility filters can reduce leakage currents normally induced by large relative earth capacitors. This filter consists of an effective branch module or impedance converter or a modified signal generator and is suitable for both three-phase and single-phase applications.

Description

  This application relates to an effective electrical filter that suppresses unwanted noise components in machine tools and industrial power tool devices. More specifically, rather than exclusively electrical filters, this application deals with electromagnetic compatibility filters on the main line or electrical supply line of an electric machine tool.

  Electromagnetic compatibility (EMC) is an increased critical factor in today's electrical and electronics industry. There are a large number of electrical circuits and instruments that are prone to radio frequency electromagnetic interference (RF EMI) or interference generated by other circuits and instruments.

  Conducted noise and disturbances in electrical devices are generally handled by inserting a low pass LC filter in the main supply line of the noise generator or noise detector. Such a filter reduces unwanted frequency components to harmless levels. Many filter topologies can be used, including class L, T and pi filter topologies.

  European Patent Application No. 1069673 (Patent Document 1) shows an example of a three-phase noise suppression filter composed of passive elements.

  Passive EMC filters have proven effective in numerous applications. However, the disadvantage of this technique is that high value capacitors and inductances are required in this application to obtain the required attenuation level. The size and price of the resulting filter is determined primarily by these large components, especially when high attenuation of common mode noise is required. Furthermore, the leakage current is directly proportional to the capacity of the filter capacitor.

  Electric machine tools present a special case with respect to leakage current problems. Especially when the machine tool is used in conjunction with a residual current device (RCD), for example a safety device at the power outlet, the safety device automatically supplies power by detecting a leakage current exceeding a defined threshold. Cut off.

  In this case, the harmless leakage current induced by EMC effectively reduces the RCD threshold in addition to the possible fault current to the machine tool ground. At this time, premature interference of the RCD follows.

  Further relationships with machine tools often cause fire protection regulations to impose a low level of allowable leakage current.

  With the EMC filter, the leakage current to ground can be reduced by reducing the value of the Y filtration capacitor. However, this severely affects the efficiency of the filter.

  Increasing the inductance value of the filter choke can compensate for the low value of the Y capacitor, but can compensate to some extent. Larger inductances have larger stray capacitors that limit attenuation, and are more expensive and bulky than conventional ones. Furthermore, the combination of large inductance and small capacitance attenuates the stability of the filter and is an undesired resonant vibration source.

The above problem is sensitive in the case of an asymmetric three-phase system, such as a system employed by a Japanese distribution grid where one of the three phases is at ground potential. Large leakage currents can be induced in this configuration from leakage in the filtration capacitor connected between the star center point and ground.
European Patent Application No. 1069673

  It is an object of the present invention to provide a machine tool EMC filter exhibiting low leakage current.

  It is a further object of the present invention to provide a machine tool EMC filter having a production cost that is lower than the production cost of known devices.

  Another object of the present invention is to provide an EMC filter for a machine tool that is more compact than known devices.

  These objects are achieved by the device which is the subject of the appended independent claims, and optional and additional useful features are introduced in the dependent claims.

  FIG. 1 represents a known type of EMC passive filter comprising a current compensation coil 15, a correlation capacitor 11, and two Y-relative earth capacitors 12. The Y capacitor 12 is effective in suppressing common mode interference transmitted to the main line, yet the capacitor is an important source of leakage current.

  According to one aspect of the invention, the EMC filter includes an effective element that suppresses unwanted RF EMI conducted by the main line without increasing leakage current as in conventional passive EMC filters. Referring to FIG. 2, the EMC filter according to the present invention comprises a current compensation coil 15 and an effective branch module 32 that represents the low impedance of the RF EMI component that is branched to ground and prevented from reaching the machine tool 31. The effectiveness of the effective branch module can be limited to the upper part of the frequency spectrum by the final response time of the electronics. In this case, two small Y capacitors that introduce negligible leakage can be added to improve high frequency attenuation.

  The EMC filter and machine tool represented in FIGS. 1 and 2 are shown as a single phase device. However, it is understood that three-phase or multi-phase devices and filters are possible and are configured within the scope of the present invention.

  An example of a valid branch module 32 is discussed with reference to FIG. This example introduces a three-phase circuit. Within the scope of the invention, it is possible to modify this three-phase circuit for a single-phase circuit. The effective branch 32 serves as a capacitor bypass for attenuating high frequency voltage components appearing in the power lines 33a, 33b and 33c and significant noise. It consists of two supplementary tracking transistors 34 that branch RF EMI by impedance 37.

  Another example of the valid branch module 32 is represented in FIG. The effective module 32 is arranged to hold the input point 72 at a potential approaching the ground potential at a frequency where undesired noise is expected. Capacitors 76a, 76b, 76c and 77a, 77b, 77c form a voltage divider for the effective branch supply coil. In this way, the active branch module is supplied with a voltage lower than the main voltage, for example half the main voltage. This reduces the fault current to harmless levels and avoids the use of fuses with large stray inductances even in the case of the destruction of some components. Furthermore, the device voltage in the effective branch is held at a level that can be managed by the capacitor divider.

  The example refers to the case of a three-phase main supply. However, the invention is not limited to this arrangement and the example can be easily modified to work with a single phase supply line.

  FIG. 4 schematically represents another embodiment of the EMC filter according to the invention. The filter consists of a negative impedance converter (NIC) 42, whereby the transformer windings 41 and 44 appear as a large series impedance in the noise appearing on the power lines 45, 45 '. The circuit of FIG. 4 allows effective filtering of EMI in the machine tool device 31 with a small Y capacitor that contributes negligibly to leakage current.

  Beneficially, in this case, the Y capacitor is entirely omitted. The NIC circuit acts as a voltage source that cancels out noise on lines 40 and 45.

  FIG. 5 shows another embodiment of the filter according to the invention which consists of current sensors 47 and 47 'and an active circuit 48 which produces a noise correcting current in the power lines 45 and 45' and which cancels out the EMI acting on the machine tool 31. Insulation between circuit 48 and supply lines 45 and 45 'is provided by insulating capacitors 49 and 49'. The current sensor 47 comprises a detection coil that reads RF EMI circulating along the supply line 45, for example.

  Furthermore, it should be understood that one of the current sensors can be omitted, and in an embodiment, only one of the lines can be sensed, even if not expressed. In another aspect, the electromagnetic coil is connected to both power lines 45 and 45 'to detect, for example, common mode noise components.

  FIG. 6 shows another embodiment of the filter of the invention in which the correction signal generated by the valid module 49 is sent to the supply lines 45 and 45 ′ by a transformer 50 that electromagnetically connects the supply lines 45 and 45 ′ to the correction signal. Represents. It should be understood that several forms of coil and wire bay are used for this purpose. In one beneficial aspect, the transformer 50 provides a current compensated impedance for the power lines 45, 45 '.

  5 and 6, the current sensor 47 and 47 'can be replaced with a transformer or a sensing capacitor as a voltage sensor. Similarly, these embodiments of the present invention could be applied for a three-phase structure.

  It is an advantage of the above embodiment that the circuit 48 is not connected in series to ground and could be completely floated as needed. In this way, the potential for stray leakage currents is further reduced.

  The inventive EMC filter is preferably included in a system consisting of a machine tool that is also connected to the main supply line, the EMC filter comprising attenuation of EMI transmitted along the supply line.

Represents a known type of EMC passive filter. 1 represents an EMC filter connected to a machine tool according to one aspect of the present invention. Fig. 3 represents an effective part of the filter of Fig. 2; Fig. 2 shows a simplified diagram of a filter comprising a negative impedance converter according to an aspect of the present invention. FIG. 2 shows a simplified diagram of a filter comprising a current detection detector according to one aspect of the present invention. 6 shows another embodiment of the filter of FIG. 3 shows another aspect of the branching module of the filter of FIG.

Explanation of symbols

11. . . . Correlation capacitor
12 . . . Y relative earth capacitor 15. . . . Current compensation coil 31. . . . Machine tool 32. . . . Effective branch module 33a, 33b, 33c. . . Electric power line 34. . . . Transistor 37. . . . Impedance 37
40. . . . Electric power line 42. . . . Negative impedance converter (NIC)
41, 44. . . Shoreline 45, 45 '. . . Power line 47, 47 '. . . Current sensor 48. . . . Active circuit 49, 49 '. . . Capacitor 50. . . . Transformer

Claims (9)

  It comprises an electric machine tool (31) and an electromagnetic compatibility filter inserted into the supply line of the electric machine tool, the electromagnetic compatibility filter comprising an active circuit for suppressing unwanted interference from the supply line. System.   The system of claim 1, wherein the electromagnetic compatibility filter includes an effective branch module (32) having at least one inductance and a low impedance of the interference.   The system according to claim 1 or 2, wherein the electromagnetic compatibility filter is arranged to suppress common mode interference transmitted to the supply line.   The system according to any one of claims 1 to 3, wherein the supply line is a single-phase or three-phase main line.   The system according to any one of the preceding claims, wherein the electromagnetic compatibility filter further comprises a relative earth capacitor (12).   The system according to any one of the preceding claims, wherein the electromagnetic compatibility filter comprises an impedance converter (42).   The electromagnetic compatibility filter comprises a transformer, wherein one of the feeders is connected in series to the supply line, and the other feeder of the transformer is connected to a negative impedance converter. Item 7. The system according to any one of Items 1 to 6.   The electromagnetic compatibility filter includes voltage or current detection means (47) for detecting a disturbance signal in the supply line, an active circuit (49, 50) for generating a correction signal based on the disturbance signal, and 8. The system according to claim 1, further comprising signal input means (49, 50) for inputting a correction signal.   9. The electromagnetic compatibility filter according to claim 1, further comprising voltage reduction means (76a, 76b, 76c) for supplying a voltage lower than the voltage of the supply line to the active circuit. System.

Images